Ca(2+) -regulated and diurnal rhythm-regulated Na(+) /Ca(2+) exchanger AtNCL affects flowering time and auxin signalling in Arabidopsis.

ABSTRACT

Calcium (Ca(2+) ) is vital for plant growth, development, hormone response and adaptation to environmental stresses, yet the mechanisms regulating plant cytosolic Ca(2+) homeostasis are not fully understood. Here, we characterize an Arabidopsis Ca(2+) -regulated Na(+) /Ca(2+) exchanger AtNCL that regulates Ca(2+) and multiple physiological processes. AtNCL was localized to the tonoplast in yeast and plant cells. AtNCL appeared to mediate sodium (Na(+) ) vacuolar sequestration and meanwhile Ca(2+) release. The EF-hand domains within AtNCL regulated Ca(2+) binding and transport of Ca(2+) and Na(+) . Plants with diminished AtNCL expression were more tolerant to high CaCl2 but more sensitive to both NaCl and auxin; heightened expression of AtNCL rendered plants more sensitive to CaCl2 but tolerant to NaCl. AtNCL expression appeared to be regulated by the diurnal rhythm and suppressed by auxin. DR5GUS expression and root responses to auxin were altered in AtNCL mutants. The auxin-induced suppression of AtNCL was attenuated in SLR/IAA14 and ARF6/8 mutants. The mutants with altered AtNCL expression also altered flowering time and FT and CO expression; FT may mediate AtNCL-regulated flowering time change. Therefore, AtNCL is a vacuolar Ca(2+) -regulated Na(+) /Ca(2+) exchanger that regulates auxin responses and flowering time.